1. Technical Field
The invention relates to a method and apparatus for screening calls in telecommunications networks and, in particular, for determining whether or not a call to a particular destination is a local call.
2. Background Art
It is usual for subscribers in a particular area to be able to make "local" calls to destinations within a Local Calling Area without incurring toll charges or for lower rates than more distant destinations. When dialling a destination number which is outside the Local Calling Area, the subscriber usually must dial the digit "1", perhaps followed by a three-digit area code, before dialling the seven-digit destination number. The central office equipment screens the dialed digits to determine whether the call is a local call or a long-distance/toll call.
In modern, stored-program central office switches, such call screening usually is performed by software which accesses a table listing 3- to 6-digit numbers determining destination numbers to which, for all subscribers in that particular area, calls will constitute local calls. The extent of the Local Calling Area is determined by the telephone company. A particular subscriber may frequently make calls to locations which are outside the Local Calling Area yet closer geographically than some locations which are within the Local Calling Area. Because they are outside the Local Calling Area, however, they incur toll charges. This can be a source of annoyance to the subscriber.
Some telephone companies may extend the Local Calling Area to include one or more additional exchanges, providing a majority of subscribers approve of the extension and agree to pay the higher basic local rates to compensate for the toll charges which otherwise would have been charged. Unfortunately, if a majority do not approve, those subscribers who did approve do not receive the extended service.